1. Field of the Invention
The present invention relates generally to an exposure apparatus and, more particularly, to a scan type exposure apparatus, suitable for manufacturing a semiconductor device or a liquid crystal display device, for performing a scan exposure while integrally holding a mask and a substrate with a carriage.
2. Related Background Art
FIG. 3 is a view schematically illustrating a construction of a typical equi-powered unit magnification projection exposure apparatus.
Referring to FIG. 3, patterns formed on a mask (unillustrated) placed on a mask stage 32 are illuminated uniformly with light beams radiated from an illumination optical system 31 and then projection-exposed on a photosensitive substrate not shown placed on a substrate stage 35 through a unit magnification (X1) projection optical system 33. The mask stage 32 and the substrate stage 35 are integrally held by a carriage 36 and scanned in an X-direction in FIG. 3 when effecting the projection exposure.
Note that the mask stage 32 is driven in X- and Y-axis directions and in a direction of rotation about a Z-axis by X-directional actuators 37, 38 and a Y-direction actuator (unillustrated) as well. Further, the illumination optical system 31 and the projection optical system 33 are held on a base board 34 fixed onto a fixed board 30.
When performing the scan-exposure, to start with, the mask and substrate are aligned with each other. That is, an alignment microscope detects an alignment mark formed on the mask and an alignment mark formed on the substrate, and the above actuators (37, 38, etc.) are driven to correct a positional deviation between the two marks.
After effecting the alignment, the carriage 36 is driven along a drive guide surface in one direction (scan direction) on the fixed board 30 by an unillustrated drive mechanism. That is, an exposure accuracy is dominated by a drive guide accuracy. Further, if there arises a necessity for slightly changing an exposure magnification by an extension and contraction of the substrate (normally, on the order of 10 ppm), oscillation drive control of the carriage 36 is executed.
On this occasion, the carriage 36 is driven while moving at least one of the mask and the substrate in the optical-axis direction (so-called focusing) or tilting it (so-called auto leveling) in accordance with a position of the carriage so that there are fixed a distance between the mask and the substrate and a relative tilt therebetween in a projection area of the projection optical system 33. Namely, the carriage 36 is driven and guided in consideration of influences by variations both in flatness of the surface of the substrate and in thickness thereof.
In the above-described conventional unit magnification projection exposure apparatus, the transfer accuracy of the mask pattern depends on the drive-guide accuracy of the carriage for integrally supporting the mask and the substrate, That is, if an attitude of the carriage changes during the scan exposure, disadvantages are caused wherein there is produced a relative positional deviation between the mask and the substrate with respect to the optical axis or projection field of the projection optical system, and the mask transfer accuracy is deteriorated.